Snuffing blast furnaces



United States Patent 0 3,099,551 ENUFFHNG BLAST FURNACES Alexander J. Macdonald, Buffalo, N.Y., assignor to National Steel Corporation, a corporation of Delaware No Drawing. Filed June 24, 1960, Ser. No. 38,427 4 Claims. (Cl. 75-4 1) The invention is concerned with blast furnace operations and, more particularly, provides an improved method for snufiing a blast furnace.

Metallurgical blast furnaces are used in the reduction of a number of metal bearing ores. iron ore, for example, is usually smelted to pig iron in a blast furnace. Iron ore, coke, and limestone are charged in consecutive order into the top of the furnace and a heated blast, the wind, is blown into the bottom of the furnace through openings at the hearth called tuyeres. The charged material, termed furnace burden or stock, descends through the furnace against the upflow of the heated blast, the ore is fused, and the iron oxide of the ore is reduced by the hot gases in the heated blast and the carbon in the coke. Temperatures encountered vary between approximately 3,500 (F. in the combustion zone at the tuyere area and approximately 400 F. at the top of the furnace.

The blast furnace operation is continuous; the furnace is charged at intervals through day and night until such time as the furnace must be shut down for repairs or for other purposes. Ideally, a furnace would operate continuously during an entire campaign, that is, from the time the furnace is built until replacement of the refractories is necessary. When the operation of a blast furnace is to be interrupted for a short period during a carnpaign, the furnace is banked. When a furnace is expected to be idle for a considerable period of time, or at the end of a campaign, the furnace is blown out.

In the standard banking procedure, the furnace remains substantially filled with burden, the blast is shut off, the tuyeres are removed, and the tuyere openings are bricked up tightly. The furnace is then carefully sealed around the tuyere breast and above, in the bosh area, to prevent infiltration of air through the joints of the brickwork or through the brickwork itself, even to the extent of painting the bosh and tuyere areas with a heavy tar or cement. The furnace is left standing in the hope that combustion will be limited or stopped. During the banked period, cooling water must continually be circulated through regular cooling means provided in the furnace walls. The banked furnace must be kept under continuous surveillance.

The end objective in blowing out is the removal of all burden from the blast furnace. In the standard blowing out procedure, previous to starting actual blowing out operations, Water sprays are installed near the top of the furnace to control the temperature of the outgoing gas in order to prevent warping of the furnace top structure. As the blowout proceeds, the blast is reduced in volume. The furnace is cut off the line when the blowout is about half completed. Water is left flowing slowly into the top of the furnace until it appears at the tuyeres. After the furnace has cooled, the burden can be raked out.

The enormity of banking and blowing out operations is commensurate with the size of the blast furnaces used today in the steel industry. From hearth to top, these furnaces measure approximately 125 feet, a normal diameter is about 28 feet, furnace volume is in excess of 50,000 cubic feet, and the materials handled in a single day may exceed 10,000 tons. The size of the blast furnace accounts for the large losses commonly incurred in banking or blowing out. Normally, throughout the present day banking operation, coke is burning. After the banked period, the coke ash must be removed before smelting op- 3,099,551 Patented July 30, 1&6?

ice

2 erations can begin. In the blowing out operation, the coke and other burden is saturated with Water and is not readily usable in subsequent smelting operations. The loss of material in either banking or blowing out will usually amount to hundreds of tons.

Though banking or blowing out are separate and distinct operations, they share one common aim, termination of combustion, that is snuffing the furnace as safely, quickly and economically as possible.

it is an object of the invention to provide an improved method for snufiing a blast furnace which offers significant savings in labor, time, and materials as well as added safety and certainty.

In a banking operation, when snufling a blast furnace by the improved method of the invention, a coke blank of 50 to 100 tons or more of coke, is charged followed by charges of ore, flux, and coke with the charges of coke being substantially higher than the normal ratio. When the first of the coke blank reaches the tuyeres, the last cast is made, draining the furnace as dry as possible, and the wind is taken off the furnace. The tuyeres are pulled and the tuyere openings, or a portion of them, may be bricked up. However, the laborious scaling up operations are completely eliminated. A gas, which will not support combustion, is introduced into the top of the furnace with sufficient pressure to force its way down through the stock. Preferably, this gas will be blast furnace gas from other operations in the mill.

The gas, as it travels down through the stock, dries the burden. The moisture from the burden, in addition to any moisture in the gas, is carried to the combustion zone where it is dissociated by the-incandescent coke. This dissociation of the moisture is a highly endothermic reaction and hastens the snuifing of the furnace.

When blast furnace gas is the gas introduced at the top of the furnace, the gas at the bottom of the furnace includes combustibles which are carried out of the furnace through the open tuyeres, if any, or unsealed crevices at the bosh and tuyere area. These combustibles exuding from the furnace are ignited for purposes of safety.

During the period when gas is being introduced at the top of the furnace and forced downwardly through the burden, analysis of the gas being introduced and the gas exiting at the bottom of the furnace is conducted. When the analyses indicate that the gases are the same, or substantially so, the furnace is out. The furnace can then stand indefinitely, unattended, and is ready to be blown in at any time. Also, when the gas analyses indicate that the fire is out, the cooling water circulation can be terminated immediately and the introduction of gas at the top of the furnace stopped.

Typical analyses are as follows:

Component Furnace Furnace Top Bosh C O 14. 8 17. O C O 25. 8 26. 8 H 3. 2 2. 8 56. 6 53. 4 00/60 1.79 1.88

Component Furnace Furnace Top Bosh 0 On 12. 2 l2. 0 O O 28. 2 28. 0 3. 6 3. 6 56. 2 5G. 2

The first analyses indicate the furnace is almost out but that combustion has not been completely terminated. The second analyses indicate that the furnace is out,

Furnace Top Component Sample #1 Sample #2 The complete absence of CO in these samples indicates there is no combustion whatsoever in the furnace.

This improved method of snuffing a blast furnace saves time and materials over the prior practice. The dry burden saves time when blowing in operations are started. Also, the moisture removed from the burden saves time in snuffing because of the rapid cooling down effected by its dissociation on the hot coals. The burden is cooler when the furnace is snuffed, the top blown gas cooling the burden as it travels downwardly putting the fire out from the top down. The snuf'rlng can be traced down the furnace by the temperature gradient on the outer shell of the furnace as the snuffing moves downwardly. Because of the relatively rapid cooling down and the thorough snuffing, the coke ash is substantially reduced over that found in the known banking methods. The savings in circulation of coolant are self-evident. The merit of the improved method also lies in the added safety and certainty during the snuffing procedure. The combustibles and other gases are carried out of the furnace and do not travel upwardly into the burden to add heat to the burden and the danger of exposion. The gas analyses provide the sure indication that the fire is out. What was formerly a hazardous, equivocal, and unwieldy operation is reduced to a safe and definite procedure.

Additional benefits are the avoidance of many of the troubles and delays that result from combustion taking place within the furnace during the usual banking operation. For one thing, the fuel is not there when it comes time to start operations vhereas with the improved method of invention, when it comes time to start production, the fuel is present in the furnace because of the rapid snufling, the desired quality iron is produce.-. faster, and there is a quicker arrival at full production. Snufrlng the furnace by the improved method also eliminates entirely the prospect of blowing out a furnace when a long term cessation of operations is planned. Previously, many furnacemen would rather blow out than bank a furnace during a long period of curtailed operations whereas by the present method, the furnace can be snuffed and left standing for long periods of time and is ready to blow in at any time.

In a blowing out operation, when snufling in accordance with the invention, coke alone may be charged so that substantially the entire burden is coke when the furnace is to be snuffed. As the wind is taken off the furnace, a gas which will not support combustion, such as blast furnace gas, is introduced into the top of the furnace. Water or steam sprays around the top of the furnace or into the furnace are neither necessary nor desirable. The gas is introduced at the top of the furnace with sufficient pressure to force its way down through the burden. The gas introduced at the top of the furnace and the gas at the bottom of the furnace are analyzed and, as previously described, when these gases have approximately the same analysis it is an indication that the furnace is out. When the furnace is out, the circulation of coolant can be terminated and the rake out of the Al. burden can be commenced immediately in preparation for relining of the furnace.

This method of snufiing the blast furnace for blowlog out punposes offers many of the advantages previously discussed in relation to the banking operation. Of great importance in this operation is the added safety presented by the improved method. The dangers of explosion present in prior art blowing out practice, due to the high hydrogen content (caused by the dissociation of water and other reasons) and encountered in the furnace, are well-known. Simply, these dangers are eliminated by the exclusion of water and the removal of gases at the bottom of the furnace. Economically of great importance, the burden is not saturated with water as in the prior art practice and can be used in subsequent furnace operations.

further advantage is that the raking out operations can be commenced as soon as the furnace is out, as the burden is cool. Perhaps the greatest advantage resulting from the improved method for snufilng a blast furnace is the elimination of the necessity for blowing out a furnace when the furnace is expected to be idle for a long period of time. The furnace can be banked for an indefinite period if snuffed in accordance with the invention and the blowing out operation can be limited to usage when reiining is necessary.

An additional complication in blowing out operations is presented by the more modern blast furnaces in which thin wall refractories, carbon linings, we used in the tuyere and bosh sections of the furnace. Normally carbon linings have twice the life of the conventional re-, fractories used from the mantle up. The problem is how to take advantage of this added life when a mantle up. relining is necessary.

Conventional blowing out processes do not solve the problem. The tuyere and bosh carbon linings are at the highest temperature found in the furnace, the Water sprays would render them useless for future operations.

When snuffing a modern carbon-lined blast furnace for purposes of blowing out, a large coke blank, normally sulllcient to ill the furnace to above the bosh area, is charged. When the coke blank reaches the tuyeres, the blast is taken off the furnace, the tuyeres are pulled, some or all of the tuyere openings may be left open, and the furnace is left unsealed. After the blast has been taken oil the furnace a gas, which will not support combustion such as blast furnace gas, is introduced at the top of the furnace with sufficient pressure to force its way down through the stock to the tuyere area. Analyses of the gas at the top and bottom of the furnace is conducted as previously described to determine when the furnace is out. No steam or water is used as in the conventional blow out. When the furnace is smothered, the burden is raked out until the stock is down to the mantle level. The burden is cool at this time and rakin out can be done safely and quickly. A platform can be constructed over the coke at the mantle level and work on removal of the brick from the mantle up can proceed with the coke in the boob and tuyere area protecting the carbon linings.

It is stressed that no water is used on the furnace during the blowing out operation and the bosh and tuyere area lining is protected during the tear out of bricks above the mantle by having the bosh full of coke. The burden raked out of the furnace is essentially as it went in and this in itself represents a substantial saving.

To summarize, the invention offers an improved method for snuflng a blast furnace by introducing a gas, such as blast furnace gas, at the [top of the furnace with sufiicient pressure to force its way down through the stock to the bottom of the furnace. Analyses of the gases at the top and bottom of the furnace provide a sure indication of when the furnace is out. The advantages over the prior practice are a savings of time and material and a safer, more certain operation.

It will be understood that certain changes in the detail", materials, and steps, herein described to explain the nature of the invention, may be resorted to Within the principle and scope of the invention as defined by the appended claims.

What is claimed is:

1. Method for snuffing a blast furnace comprising the steps of introducing blast furnace gas at the top of the furnace with sufficient pressure to force its way down through furnace stock to the bottom of the furnace, analyzing the blast furnace gas introduced at the top of the furnace and gas at the bottom of the furnace, terminating the introduction of gas when the analyses of the blast furnace introduced gas at the top of the furnace and the gas at the bottom of the furnace are approximately the same indicating that the furnace is out, and conducting an analysis of the draft gases through the furnace to determine if any CO is present in the furnace thereby conclusively determining that the furnace is out.

2. Method for snufiing a blast furnace in which ore and fuel are charged into the top of the furnace and a hot-blast is introduced through tuyeres into the bottom of the furnace comprising the steps of charging a coke blank into the top of the furnace, terminating the hotblast when :the coke blank reaches the tuyere area, introducing blast furnace gas into the top of the furnace with suflicient pressure to force its way down through furnace stock to the tuyere area, analyzing the gas introduced and the gas at the tuyere area, and terminating the introduction of blast furnace gas when analysis of the gas introduced at the top of the furnace and the gas at [the tuyere area are approximately the same indicating that the furnace is out.

3. Method for snuffing a blast furnace in which ore and fuel are charged into the top of the furnace, a hotbl ast is introduced through tuyeres into the bottom of the furnace, and a coolant flows in heat exchange relationship with furnace Wall structure comprising the steps of charging a coke blank into the top of the furnace, terminating the hot-blast when the coke blank reaches the tuyeres, introducing blast furnace gas into the top of the furnace with sufiicient pressure to force its way down through furnace stock to the tuyere area, igniting gas exuding from the furnace at and above the tuyere area, analyzing the gas introduced at the top of the furnace and gas at the tuyere area, terminating introduction of gas and coolant flow when the gas analyses at the top and bottom of the furnace are substantially the same, and conducting an analysis of the natural draft gases through the furnace to determine if CO is present in the furnace and thereby establish that the furnace is out.

4. Method for snuffing a carbon-lined blast furnace for a mantle-up relining operation comprising the steps of charging a coke blank sufficient to fill the furnace to above its bosh area, terminating hot blast to the furnace when the coke blank reaches the blast furnace tuyere area, introducing blast furnace gas into the blast furnace top with sufficient pressure to force its way down through the coke blank and exit at the tuyere area, analyzing the blast gas introduced at the blast furnace top and gas exiting from the furnace at the tuyere area, terminating introduction of blast furnace gas at the top of the furnace when the blast furnace gas and exiting gas analyses are approximately the same, and thereafter testing natural draft gas exiting from the blast furnace top for carbon monoxide to determine conclusively that the furnace is out. 7

References Cited in the file of this patent A.I.M.M.E., Blast Furnace, Coke Oven, and Raw Materials Committee, Proceedings, vol. 10, 1951, pages 200 to 2'18. 

4. METHOD FOR SNUFFING A CARBON-LINED BLAST FURNACE FOR A MANTEL-UP RELINING OPERATION COMPRISING THE STEPS OF CHARGING A COKE BLANK SUFFICIENT TO FILL THE FURNACE TO ABOVE ITS BOSH AREA, TERMINATING HOT BLAST TO THE FURNACE WHEN THE COKE BLANK REACHES THE BLAST FURNACE TUYERE AREA, INTRODUCING BLAST FURNACE GAS INTO THE BLAST FURNACE TOP WITH SUFFICIENT PRESSURE TO FORCE ITS WAY DOWM THROUGH THE COKE BLANK AND EXIT AT THE TUYERE AREA, ANALYZING THE BLAST GAS INTRODUCED AT THE BLAST FURNACE TOP AND GAS EXISTING FROM THE FURNACE AT THE TUYERE AREA, TERMINATING INTRODUCTION OF BLAST FURNACE GAS AT THE TOP OF THE FURNACE WHEN THE BLAST FURNACE GAS AND EXITING GAS ANALYSES ARE APPROXIMATELY THE SAME, AND THEREAFTER TESTING NATURAL DRAFT GAS EXITING FROM THE BLAST FURNACE TOP FOR CARBON MONOXIDE TO DETERMINE CONCLUSIVELY THAT THE FURNACE IS OUT. 